The present invention is directed to a system and method for controlling an electro-hydraulic valve arrangement. In particular, the present invention is directed to a system and method for controlling an electro-hydraulic valve arrangement to perform a pump check function.
Hydraulic actuators, such as piston/cylinder arrangements or fluid motors, are commonly used to move work implements, such as, for example, buckets, shovels, loaders, backhoes, rakes, trenchers, forklifts, etc., that are carried on work machines. The hydraulic actuators provide the power necessary to move the work implement to accomplish an operation. Depending on the type of work implement and the requirements of the work machine, one or more hydraulic actuator may be connected to the work implement.
Each hydraulic actuator typically includes at least two fluid chambers that are disposed on opposite sides of a moveable element. The moveable element of each hydraulic actuator is, in turn, connected to the work implement that is to be moved. The work machine usually carries a pump that is connected to the hydraulic actuator and provides pressurized fluid to one or the other of the fluid chambers of the hydraulic actuator. Typically, an electro-hydraulic valve arrangement is placed in fluid connection between the pump and the hydraulic actuator to control a flow rate and direction of pressurized fluid to and from the fluid chambers.
When it is desirable to move the work implement in a certain direction, the electro-hydraulic valve arrangement is moved to place the pump in fluid connection with one chamber of the hydraulic actuator at the same time that fluid is allowed to flow out of the other chamber. This creates a pressure differential over the moveable element of the hydraulic actuator. Provided that the force exerted on the moveable element by the pressurized fluid is great enough to overcome the resistant force of the work implement, the moveable element will move towards the area of lower fluid pressure existing in the opposite chamber of the hydraulic actuator, thereby moving the work implement.
If however, the pressure of the fluid leaving the pump is less than the pressure of the fluid in the hydraulic actuator, the fluid will tend to flow from the actuator towards the pump, i.e. in a reverse direction. If the fluid were allowed to flow unchecked, the moveable element of the hydraulic actuator would move in an undesirable manner.
Typically, as shown in U.S. Pat. No. 4,967,557, a mechanical check valve is disposed in the fluid connection between the pump and the electro-hydraulic valve arrangement. The mechanical check valve is a spring loaded valve that only allows fluid to flow in one direction, e.g., from the pump to the electro-hydraulic valve arrangement. When the pressure differential over the check valve is positive, i.e. the pressure of the fluid on a first side of the valve is greater that the pressure of the fluid on the opposite side of the valve, the force of the fluid will overcome the spring force and open the check valve. If, however, the pressure of the fluid on the first side of the valve is less than the pressure on the opposite side of the valve, the valve will close and prevent fluid from flowing through the valve.
The use of mechanical check valves to perform the pump and load check functions may be disadvantageous to the overall system. For instance, each mechanical check valve may add cost to the overall system. In addition, the inclusion of a mechanical check valve may increase the size of the overall system.
The present invention provides a system and method for controlling an electro-hydraulic valve arrangement that solves all or some of the problems set forth above.
To attain the advantages in accordance with the purposes of the invention, as embodied and broadly described herein, the invention is directed to a method of controlling an electro-hydraulic valve arrangement that is disposed in fluid connection between a source of pressurized fluid and an actuator. According to the method, a signal is received to open the electro-hydraulic valve arrangement to provide a flow of fluid from the source of pressurized fluid to the actuator. A source pressure that is representative of the pressure of fluid between the source of pressurized fluid and the electro-hydraulic valve arrangement is determined. An actuator pressure that is representative of the pressure of the fluid between the electro-hydraulic valve arrangement and the actuator is also determined. The generated signal is modified to prevent the electro-hydraulic valve arrangement from opening when the source pressure is less than the actuator pressure to prevent a reverse flow of fluid from the actuator to the source of pressurized fluid.
In another aspect, the invention is directed to a system for controlling a hydraulic actuator that includes a hydraulic actuator and a source of pressurized fluid. An electro-hydraulic valve arrangement is positioned in fluid connection with the source of pressurized fluid and the hydraulic actuator and is operable to control a flow rate of fluid from the source of pressurized fluid to the hydraulic actuator. A first pressure sensor senses a source pressure that is representative of the pressure of the fluid between the source of pressurized fluid and the electro-hydraulic valve arrangement. A second pressure sensor senses an actuator pressure that is representative of the pressure of the fluid between the electro-hydraulic valve arrangement and the hydraulic actuator. A control device receives a signal to open the electro-hydraulic valve arrangement and prevents the electro-hydraulic valve arrangement from opening when the source pressure is less than the actuator pressure.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.